Isn't it just possible that readers are simply tiring of the same old sh!t after that many books with the same characters/settings?

No. I grabbed early versions of 2 of the authors books and found the characters more human and interesting, the descriptions more colorful, much tighter plots. I enjoyed the early books after reading latest works that disappointed. It's almost like the later books are written by a different author. I suspect what really happens is the early books were gone over by copy-editors or proof-readers and things were tightened up. (This is the one good thing about re-buying my library for the ereader.)